Methods of gate replacement in semiconductor devices

ABSTRACT

A method of forming a semiconductor device includes forming a plurality of fins on a substrate, forming a polysilicon gate structure, and replacing the polysilicon gate structure with a metal gate structure. Replacing the polysilicon gate structure includes depositing a work function metal layer over the plurality of fins, forming a metal oxide layer over the work function metal layer, and depositing a first metal layer over the metal oxide layer. A first portion of the metal oxide layer is formed within an area between adjacent fins from among the plurality of fins. An example benefit includes reduced diffusion of unwanted and/or detrimental elements from the first metal layer into its underlying layers and consequently, the reduction of the negative impact of these unwanted and/or detrimental elements on the semiconductor device performance.

BACKGROUND

This disclosure generally relates to semiconductor devices and methodsof fabricating the same.

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and finFETs.

Such scaling down has increased the complexity of semiconductormanufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an isometric view of an exemplary finFET.

FIG. 2 is a cross-sectional view of an exemplary finFET.

FIGS. 3-8, 9A-15A, and 9B-15B are views of a finFET at various stages ofits exemplary fabrication process.

FIG. 16 is an exemplary transmission electron microscopy (TEM) image ofa cross-section of an exemplary test structure.

FIG. 17 is a TEM image of a cross-section of a test structure.

FIGS. 18-19 are exemplary energy-dispersive X-ray spectroscopy (EDX)images of a cross-section of exemplary finFET.

FIG. 20 is a flow diagram of an exemplary method for fabricating afinFET.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Asused herein, the formation of a first feature on a second feature meansthe first feature is formed in direct contact with the second feature.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesdo not necessarily refer to the same embodiment. Further, when aparticular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

The term “about” as used herein indicates the value of a given quantityvaries by ±10% of the value, or optionally ±5% of the value, or in someembodiments, by ±1% of the value so described. For example, “about 100nm” encompasses a range from 90 nm to 110 nm, inclusive.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

As used herein, the term “selectivity” refers to the ratio of the etchrates of two materials under the same etching conditions.

As used herein the term “substrate” describes a material onto whichsubsequent material layers are added. The substrate itself may bepatterned, and materials added on top of it may also be patterned, ormay remain without patterning. Furthermore, “substrate” may be any of awide array of semiconductor materials such as silicon, germanium,gallium arsenide, indium phosphide, etc. Alternatively, the substratemay be electrically non-conductive such as a glass or sapphire wafer.

An Exemplary FinFET

FIG. 1 is an isometric view of an exemplary finFET 100 taken after agate replacement process. FinFET 100 refers to any fin-based, multi-gatetransistor. FinFET 100 may be included in a microprocessor, memory cell,and/or other integrated circuit (IC). Although FIG. 1 illustrates finFET100, it is understood the IC may comprise any number of other devicescomprising resistors, capacitors, inductors, fuses, etc. FIG. 1 is forillustrative purposes and is not drawn to scale.

FinFET 100 is formed on a substrate 102, and includes a plurality offins 104.1 through 104.3, a plurality of shallow trench isolation (STI)regions 106, a gate structure 108 disposed on each of fins 104.1 through104.3, spacers 120, a source/drain region 112 disposed on one side ofgate structure 108, and a source/drain region 114 disposed on anotherside of gate structure 108. It is understood by those skilled in therelevant art(s) that the names “source” and “drain” can beinterchangeable based on the voltage that is applied to those terminalswhen the transistor is operated. FIG. 1 shows one gate structure 108.However, there may be additional gate structure(s) (not shown) similarand parallel to gate structure 108. In addition, finFET 100 may includeother components such as source/drain contacts, gate contacts, vias,interconnect metal layers, dielectric layers, passivation layers, etc.that, for the sake of clarity, are not shown. The isometric view of FIG.1 is taken after formation of gate structure 108 in a gate replacementprocess.

Substrate 102 represents a physical material on which finFET 100 isformed. Substrate 102 is a semiconductor material such as, but notlimited to, silicon. In some embodiments, substrate 102 comprises acrystalline silicon substrate (e.g., wafer). In some embodiments,substrate 102 comprises another elementary semiconductor, such asdiamond or germanium; a compound semiconductor including siliconcarbide, gallium arsenide, gallium phosphide, indium phosphide, indiumarsenide, and/or indium antimonide; an alloy semiconductor includingsilicon germanium carbide, silicon germanium, gallium arsenic phosphide,gallium indium phosphide, gallium indium arsenide, gallium indiumarsenic phosphide, aluminum indium arsenide, and/or aluminum galliumarsenide; or combinations thereof. Yet in some embodiments, substrate102 includes an epitaxial layer (epi-layer), may be strained forperformance enhancement, and/or includes a silicon-on-insulator (SOI)structure. Further, substrate 102 may be doped depending on designrequirements (e.g., p-type substrate or n-type substrate). In someembodiments, substrate 102 may be doped with p-type dopants, such asboron or n-type dopants, such as phosphorus or arsenic. The dopedsubstrate 102 may be configured for an n-type finFET, or alternativelyconfigured for a p-type finFET.

Fins 104.1 through 104.3 represent current carrying structures of finFET100. Fins 104.1, 104.2, and 104.3 include channel regions (not shown inFIG. 1; a cross-sectional view of channel region 130.3 corresponding tofin 104.3 is shown in FIG. 9A). Each of the channel regions underliesgate structure 108 and is disposed between source/drain regions 112 and114. Channel regions provide conductive paths between source/drainregions 112 and 114 when a voltage applied to gate structure 108 turnson finFET 100. It should be noted that finFET 100 is shown in FIG. 1 asincluding three fins 104.1 through 104.3 for the sake of simplicity.However, as would be understood by a person of skill in the art(s),finFET 100 may include any suitable number of fins. This suitable numbercan include a single fin as well as multiple fins similar to thoseillustrated in FIG. 1.

STI regions 106 provide electrical isolation of finFET 100 fromneighboring active and passive elements (not illustrated in FIG. 1)integrated with or deposited onto substrate 102. Additionally, STIregions 106 provide electrical isolation between each of fins 104.1through 104.3 and/or between fins 104.1 through 104.3 and theneighboring active and passive elements. STI regions 106 are made ofdielectric material. In some embodiments, STI regions 106 includessilicon oxide, silicon nitride, silicon oxynitride, fluorine-dopedsilicate glass (FSG), a low-k dielectric material, and/or other suitableinsulating material. In some embodiments, STI regions 106 include amulti-layer structure, for example, having one or more liner layers.

FinFET 100 further includes an interface 121 between fins 104.1 through104.3 and source/drain regions 112 and 114 and an interface 123 betweenSTI regions 106 and substrate 102. In some embodiments, interface 121 iscoplanar with interface 123. In some embodiments, interface 121 iseither above or below interface 123. In some embodiments, interface 121is above the level of the top surface of STI regions 106.

Source/drain regions 112 and 114 are formed on fins 104.1 through 104.3.Source/drain regions 112 and 114 include epitaxially grown semiconductormaterial on recessed portions of fins 104.1 through 104.3 on either sideof gate structure 108. In some embodiments, the epitaxially grownsemiconductor material is the same material as the material of substrate102. In some embodiments, the epitaxially grown semiconductor materialis a strained semiconductor material that includes a different materialfrom the material of substrate 102. Since the lattice constant of thestrained semiconductor material is different from the material ofsubstrate 102, channel regions are strained or stressed toadvantageously increase carrier mobility in the channel region of finFET100 and thereby enhance its performance. The strained semiconductormaterial may include element semiconductor material such as germanium(Ge) or silicon (Si); or compound semiconductor materials, such asgallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs); orsemiconductor alloy, such as silicon germanium (SiGe), gallium arsenidephosphide (GaAsP).

Further, source/drain regions 112 and 114 may be in-situ doped duringthe epi process. In various embodiments, the epitaxially grownsource/drain regions 112 and 114 may be doped with p-type dopants, suchas boron or BF₂; n-type dopants, such as phosphorus or arsenic; and/orcombinations thereof; epitaxially grown strained SiGe source/drainregions 112 and 114 may be doped with p-type dopants, such as boron orBF₂, n-type dopants, such as phosphorus or arsenic, and/or combinationsthereof; epitaxially grown Si source/drain regions 112 and 114 may bedoped with carbon to form Si:C source/drain regions 112 and 114,phosphorous to form Si:P source/drain regions 112 and 114, or bothcarbon and phosphorous to form SiCP source/drain regions 112 and 114. Insome embodiments, source/drain regions 112 and 114 are not in-situdoped, and an implantation process (i.e., a junction implant process) isperformed to dope source/drain regions 112 and 114.

Gate structure 108 traverses each of fins 104.1 through 104.3 and wrapsaround a portion of each of fins 104.1 through 104.3 defining thechannel regions between source/drain regions 112 and 114. Gate structure108 controls the current flowing between source/drain regions 112 and114 through the channel regions. Gate structure 108 includes adielectric layer 116 and a gate electrode 118. In some embodiments,dielectric layer 116 is adjacent to and in contact with gate electrode118. In some embodiments, a thickness 116 t of dielectric layer 116 isin the range of about 1 nm to about 5 nm. Gate structure 108 may furtherinclude interfacial layers at interface between gate structure 108 andfins 104.1 through 104.3, capping layers, etch stop layers, and/or othersuitable materials in various embodiments. The interfacial layers mayinclude a dielectric material such as a silicon dioxide layer (SiO₂) orsilicon oxynitride (SiON) and help to reduce damage between gatestructure 108 and fins 104.1 through 104.3. The interfacial dielectriclayers may be formed by chemical oxidation, thermal oxidation, atomiclayer deposition (ALD), chemical vapor deposition (CVD), and/or othersuitable formation processes.

Dielectric layer 116 traverses each of fins 104.1 through 104.3 andwraps around a portion of each of fins 104.1 through 104.3 asillustrated in FIG. 2. FIG. 2 is a cross-sectional view of finFET 100along line A-A in FIG. 1 in accordance with various embodiments.Dielectric layer 116 may include silicon oxide formed by CVD, ALD,physical vapor deposition (PVD), e-beam evaporation, or other suitableprocess. In some embodiments, dielectric layer 116 includes one or morelayers of silicon oxide, silicon nitride, silicon oxy-nitride, or high-kdielectric materials such as hafnium oxide (HfO₂), TiO₂, HfZrO, Ta₂O₃,HfSiO₄, ZrO₂, ZrSiO₂, or combinations thereof. Alternatively, high-kdielectric materials may comprise metal oxides. Examples of metal oxidesused for high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y,Zr, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and/ormixtures thereof. The high-k dielectric layer may be formed by ALDand/or other suitable methods. In some embodiments, dielectric layer 116includes a single layer or a stack of insulating material layers.Spacers 120 are in substantial contact with dielectric layer 116.

Referring to FIG. 2, gate electrode 118 may include a gate work functionmetal layer 222, a gate metal fill layer 224, and gate metal oxide layer226, as illustrated in FIG. 2. FIG. 2 is a cross-sectional view offinFET 100 along line A-A in FIG. 1 in accordance with variousembodiments. The cross-sectional view is taken after the formation ofdielectric layer 116 and gate electrode 118 in a gate replacementprocess. It should be noted that the exemplary illustration of finFET100 in FIG. 1 and the exemplary illustration of finFET 100 along lineA-A in FIG. 2 may not be to scale. Those skilled in the relevant artwill recognize that FIG. 2 is intended to describe additional structuresof finFET 100 as well as further describe those structures of finFET 100that are illustrated in FIG. 1. Those skilled in the relevant art willadditionally recognize that finFET 100 need not include all of theadditional structures of finFET 100 as illustrated in FIG. 2 withoutdeparting from the spirit and scope of this disclosure. Rather,different structures, configurations, and arrangements, as well asdifferent configurations and arrangements for the structures describedin FIGS. 1 and 2 are possible for finFET 100.

In some embodiments, gate work function metal layer 222 is disposed ondielectric layer 116. Gate work function metal layer 222 may include asingle metallic layer or a stack of metallic layers. The stack ofmetallic layers may include metals having work functions similar to ordifferent from each other. In some embodiments, gate work function metallayer 222 includes any suitable material, such as aluminum (Al), copper(Cu), tungsten (W), titanium (Ti), tantalum (Ta), titanium nitride(TiN), tantalum nitride (TaN), nickel silicide cobalt silicide (CoSi),silver (Ag), TaC, TaSiN, TaCN, TiAl, TiAlN, WN, metal alloys, and/orcombinations thereof. Exemplary work function metal(s) that may beincluded in gate work function metal layer 222 in a p-type deviceinclude TiN, TaN, Ru, Mo, Al, WN, ZrSi2, MoSi2, TaSi2, NiSi2, WN, othersuitable p-type work function metals, or combinations thereof. Exemplarywork function metal(s) that may be included in work function metal layer222 in an n-type device include Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN,TaSiN, Mn, Zr, other suitable n-type work function materials, orcombinations thereof. Gate work function metal layer 222 may be formedusing a suitable process such as ALD, CVD, PVD, plating, or combinationsthereof. In some embodiments, a thickness 222 t of gate work functionmetal layer 222 is in the range of about 2 nm to about 15 nm.

Gate work function metal layer 222 is one of the factors that controlsthe finFET threshold voltage and thus the current flow betweensource/drain regions 112 and 114. A work function is associated with thecomposition of the one or more metals included in gate work functionmetal layer 222. The one or more metals are chosen to determine the workfunction of gate work function metal layer 222 so that a desiredthreshold voltage is achieved. In some embodiments, the work function ofthe one or more metals is in the range of about 4 eV to about 6 eV.

Gate metal fill layer 224 may include a single metal layer or a stack ofmetallic layers. The stack of metallic layers may include metalsdifferent from each other. In some embodiments, gate metal fill layer224 includes any suitable conductive material, such as Ti, Ag, Al,TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, WN, Cu, W, Co, Ni,TiC, TiAlC, TaAlC, metal alloys, and/or combinations thereof. Gate metalfill layer 224 may be formed by AT D, PVD, CVL), or other suitableconductive material deposition process. In an embodiment, gate metalfill layer 224 includes W film formed by ALD or CVD. The W film mayinclude fluorine in the form of fluoride ions introduced from afluorine-based precursor (e.g., tungsten hexafluoride (WF₆)) used duringthe W film deposition process. In another embodiment, gate metal filllayer 224 includes Al or Co film formed by ALD or CVD.

Typically, current devices having W, Al, Co, or other suitable metalsincluded in gate metal fill layers in gate electrodes suffer from poordevice performance due to diffusion of fluorine from W, Al from Al, Co,or other elements from other suitable metals into one or more underlyinglayers such as gate work function metal layers (e.g., gate work functionmetal layer 222), dielectric layers (e.g., dielectric layer 116), fins(e.g., fins 104.1 through 104.3), and/or other layers and/or structuresof the current devices. The presence of such contaminants inconsiderable amount adversely affects the chemical and physicalproperties of the materials of the underlying layers of the currentdevices. For example, diffusion of fluorine contaminants into underlyinggate work function metal layers can negatively affect the work functionvalue of the one or more metals included in the gate work function metallayers of current devices, and consequently, have negative effect on thecontrol and tuning of the threshold voltage of the current devices.

In order to prevent and/or reduce the diffusion of unwanted elementsfrom gate metal fill layers into underlying layer(s) and/or structure(s)of the current devices, the present disclosure describes passivationlayers such as gate metal oxide layer 226, according to variousembodiments. Gate metal oxide layer 226 may be interposed between gatemetal fill layer 224 and gate work function metal layer 222. In oneembodiment of finFET 100, gate metal oxide layer 226 covers surfaceareas underlying gate metal fill layer 224. In another embodiment, gatemetal oxide layer 226 may partially or completely fill the areas betweenfins 104.1 through 104.3 such as areas 230 and/or 232. In someembodiments, top surface portion 226 a of gate metal oxide layer 226within area 230 and/or top surface portion 226 b of gate metal oxidelayer 226 is below or coplanar with top surface portion 226 s of gatemetal oxide layer 226, top surface portion 222 s of gate work functionmetal layer 222, top surface portion 116 s of dielectric layer 116, ortop surfaces 104 s of fins 104.1 through 104.3. Top surface portions 226s, 222 s, 116 s are surface portions that are disposed over fins 104.1through 104.3. In some embodiments, top surface portions 226 a and/or226 b are above surface 222 s, surface 116 s, or top surface 104 s. Gatemetal oxide layer 226 may include voids or air pockets of differentshapes and sizes such as voids or air pockets 234. Even though voids orair pockets 234 are illustrated to be included only in a portion of gatemetal oxide layer 226 within area 230, the present disclosure is notlimited to this illustration. Voids or air pockets of any shape and sizeand in any number may be formed in any portion of gate metal oxide layer226. In some embodiments, gate metal oxide layer 226 is a continuouslayer and does not include voids or air pockets. In some embodiments,gate metal oxide layer 226 is formed only within areas 230 and 232 andnot over STI regions 106 and fins 104.1 through 104.3 (not shown).

Presence of gate metal oxide layer 226 reduces the diffusion surfacearea for unwanted and/or detrimental elements to diffuse from gate metalfill layer 224 into one or more layers underlying gate metal oxide layer226. Consequently, gate metal oxide layers 226 helps to prevent and/orreduce the diffusion of unwanted and/or detrimental elements from gatemetal fill layer 224 into one or more underlying layers such as gatework function metal layer 222, dielectric layer 116, fins 104.1 through104.3, and/or source/drain regions 112 and 114 during subsequentprocessing of finFET 100. Gate metal oxide layer 226 may include anysuitable metal oxide such as oxides of W, Al, Co, Ti, Ag, Mn, Zr, Cu,Ni, and/or combinations thereof. The one or more materials included ingate metal oxide layer 226 may be selected based on their property andability to hinder or prevent diffusion of the unwanted elements fromgate metal fill layer 224 into the one or more layers underlying gatemetal oxide layer 226. In some embodiments, thickness 226 t of gatemetal oxide layer 226 over fins 104.1 through 104.3 and STI regions 106ranges from about 0.5 nm to about 1 nm.

Referring to FIG. 2, additionally or optionally, gate electrode 118includes a gate metal liner 228 interposed between gate work functionmetal layer 222 and gate metal oxide layer 226 in some embodiments. Gatemetal liner 228 may be disposed on gate work function metal layer 222.Gate metal liner 228 may include any suitable metal such as W, Al, Co,Ti, Ag, Mn, Zr, Cu, Ni, and/or combinations thereof and may be formed byALD, PVD, CVD, or other suitable metal deposition process.

Gate metal liner 228 may serve as a metal precursor for the formation ofgate metal oxide layer 226. Gate metal oxide layer 226 may be formed byoxidizing gate metal liner 228 using any suitable oxidation process suchas, but not limited to, air oxidation (i.e., exposure to air), O₂ plasmaprocess, or a wet or dry thermal oxidation in an ambient comprising anoxide, H₂O, NO, or a combination thereof. In some embodiments, gatemetal liner 228 is deposited in a deposition chamber and exposed to airby breaking vacuum in the deposition chamber after the deposition toform gate metal oxide layer 226. In some embodiments, gate metal liner228 is deposited in a deposition chamber and thermally oxidized to gatemetal oxide layer 226 at an oxidation temperature of the materialincluded in gate metal liner 228. In some embodiments, surface and/orseveral topmost atomic layers of gate metal liner 228 is oxidized toform gate metal oxide layer 226. In other embodiments, gate metal liner228 is completely oxidized to form gate metal oxide layer 226, which isdisposed on gate work function metal layer 222 (not shown).

An Example Method for Fabricating a FinFET

FIGS. 3-8 are isometric views of finFET 100 (as illustrated in FIGS. 1and 2) at various stages of its exemplary fabrication. FIGS. 9A-15A andFIGS. 9B-15B are cross-sectional views along line A-A and line B-B,respectively, of finFET 100 of FIG. 1 at various stages of its exemplaryfabrication.

FIG. 3 is an isometric view of a partially fabricated finFET 100 afterpatterning of photoresist on substrate 102 for formation of fins 104.1through 104.3. Fins 104.1 through 104.3 are formed by etching intosubstrate 102. A pad layer 336 a and a mask layer 336 b are formed onsubstrate 102. Pad layer 336 a may be a thin film comprising siliconoxide formed, for example, using a thermal oxidation process. Pad layer336 a may act as an adhesion layer between substrate 102 and mask layer336 b. Pad layer 336 a may also act as an etch stop layer for etchingmask layer 336 b. In an embodiment, mask layer 336 b is formed ofsilicon nitride, for example, using low pressure chemical vapordeposition (LPCVD) or plasma enhanced CVD (PECVD). Mask layer 336 b isused as a hard mask during subsequent photolithography processes. Aphotoresist layer 338 is formed on mask layer 336 b and is thenpatterned, forming openings 340 in photo-sensitive layer 338.

FIG. 4 is an isometric view of a partially fabricated finFET 100 afterthe exemplary formation of fins 104.1 through 104.3. Mask layer 336 band pad layer 336 a are etched through openings 340 to expose underlyingsubstrate 102. The exposed substrate 102 is then etched to form trenches442 with top surfaces 102 s of substrate 102. Portions of substrate 102between trenches 442 form fins 104.1 through 104.3. Patternedphotoresist 338 is then removed. Next, a cleaning may be performed toremove a native oxide of substrate 102. The cleaning may be performedusing diluted hydrofluoric (DHF) acid. In some embodiments, trenches 442are spaced apart from adjacent trenches by a spacing S (i.e., finwidths) smaller than about 30 nm and depth D of trenches 442 ranges fromabout 210 nm to about 250 nm while width W (i.e., fin spacing) oftrenches 442 is less than 50 nm. In some embodiments, the aspect ratio(D/W) of trenches 442 is greater than about 7.0. In other embodiments,the aspect ratio may even be greater than about 8.0. In yet otherembodiments, the aspect ratio is lower than about 7.0.

FIG. 5 is an isometric view of a partially fabricated finFET 100 afterthe exemplary formation of STI regions 106. The formation of STI regions106 involves deposition and etching of a dielectric material. Trenches442 are filled with a dielectric material. The dielectric material mayinclude silicon oxide. In some embodiments, other dielectric materials,such as silicon nitride, silicon oxynitride, fluoride-doped silicateglass (FSG), or a low-k dielectric material, may also be used. In someembodiments, the dielectric material may be formed using a flowable CVD(FCVD) process, a high-density-plasma (HDP) CVD process, using silane(SiH₄) and oxygen (O₂) as reacting precursors. In other embodiments, thedielectric material may be formed using a sub-atmospheric CVD (SACVD)process or high aspect-ratio process (HARP), wherein process gases maycomprise tetraethoxysilane (TEOS) and/or ozone (O₃). In otherembodiments, the dielectric material may be formed using aspin-on-dielectric (SOD) such as hydrogen silsesquioxane (HSQ) or methylsilsesquioxane (MSQ).

A chemical mechanical polish or a wet etch process is then performed forthe removal of mask layer 336 b and pad layer 336 a. This removal isfollowed by an etching of the dielectric material to form STI regions106 and recessed regions 544 as shown in FIG. 5. Etching of thedielectric material may be performed using a wet etching process, forexample, by dipping substrate 102 in hydrofluoric acid (HF).Alternatively, the etching operation may be performed using a dryetching process, for example, using CHF₃ or BF₃ as etching gases. Upperfin portions 546.1 through 546.3 of fins 104.1 through 104.3,respectively, protruding over flat top surfaces 106 t of STI regions 106are used to form channel regions of finFET 100. Upper fin portions 546.1through 546.3 may comprise top surfaces 546.1 t through 546.3 t,respectively. In some embodiments, flat top surfaces 106 t of STIregions 106 are lower than top surfaces 546.1 t through 546.3 t. In anembodiment, a vertical dimension of each of the upper fin portions 546.1through 546.3 ranges from about 15 nm to about 50 nm. In anotherembodiment, a vertical dimension of each of the upper fin portions 546.1through 546.3 ranges from about 20 nm to about 40 nm. Yet in anotherembodiment, a vertical dimension of each of the upper fin portions 546.1through 546.3 ranges from about 25 nm to about 35 nm.

FIG. 6 is an isometric view of a partially fabricated finFET 100 afterthe exemplary formation of a structure 648 on fins 104.1 through 104.3and STI regions 106. Structure 648 includes a patterned polysiliconstructure 650 and spacers 120. Patterned polysilicon structure 650 andspacers 120 are formed over top surfaces 106 t of STI regions 106 andover top surfaces 546.1 t through 546.3 t to wrap around upper finportions 546.1 through 546.3. Interfaces 652 are formed between upperfin portions 546.1 through 546.3 and patterned polysilicon structure 650and spacers 120. Patterned polysilicon structure 650 is formed by anysuitable process or processes. For example, patterned polysiliconstructure 650 can be formed by a procedure including deposition,photolithography patterning, and etching processes. The depositionprocesses include CVD, PVD, ALD, other suitable methods, and/orcombinations thereof. The photolithography patterning processes includephotoresist coating (e.g., spin-on coating), soft baking, mask aligning,exposure, post-exposure baking, developing the photoresist, rinsing,drying (e.g., hard baking), other suitable processes, and/orcombinations thereof. The etching processes include dry etching, wetetching, and/or other etching methods (e.g., reactive ion etching).Spacers 120 may include dielectric material such as silicon oxide,silicon carbide, silicon nitride, silicon oxy-nitride, or other suitablematerial. Spacers 120 may comprise a single layer or multilayerstructure. A blanket layer of a dielectric material may be formed overpatterned polysilicon structure 650 by CVD, PVD, ALD, or other suitabletechnique followed by an anisotropic etching on the dielectric materialto form spacers 120 on two sides of patterned polysilicon structure 650.Each of spacers 120 comprises a thickness 120 t in a range from about 5nm to about 15 nm.

FIG. 7 is an isometric view of a partially fabricated finFET 100 afterthe exemplary formation of recessed fin portions 754 of fins 104.1through 104.3. The portions of fins 104.1 through 104.3 that are notcovered by structure 648 are recessed to form recessed fin portions 754of fins 104.1 through 104.3 having surfaces 104 t. In an embodiment,surfaces 104 t of recessed fin portions 754 are below the flat topsurfaces 106 t of STI regions 106. In alternative embodiments, theportions of fins 104.1 through 104.3 that are not covered by structure648 are recessed to expose top surface 102 s of substrate 102. In oneembodiment, using spacers 120 as masks, a biased etching process isperformed to form recessed fin portions 754. The etching process may beperformed under a pressure of about 1 mTorr to about 1000 mTorr, a powerof about 50 W to about 1000 W, a bias voltage of about 20 V to about 500V, at a temperature of about 40° C. to about 60° C., and using a HBrand/or Cl₂ as etch gases. Also, the bias voltage used in the etchingprocess may be tuned to allow better control of an etching direction toachieve desired profiles for recessed fin portions 754.

FIG. 8 is an isometric view of a partially fabricated finFET 100 afterthe exemplary formation of source/drain regions 112 and 114 on recessedfin portions 754 of fins 104.1 through 104.3. Source/drain regions 112and 114 include epitaxially grown semiconductor material on recessedportions 754 of fins 104.1 through 104.3. Semiconductor material ofsource/drain regions 112 and 114 is selectively epitaxially grown overrecessed portions 754. In some embodiments, the selective epitaxialgrowth of the semiconductor material of source/drain regions 112 and 114continues until the semiconductor material extends vertically a distancein a range from about 10 nm to about 100 nm above top surface 102 s ofsubstrate 102 and extends laterally over top surfaces 106 t of some ofthe STI regions 106. The semiconductor material includes elementsemiconductor material such as germanium (Ge) or silicon (Si); orcompound semiconductor materials, such as gallium arsenide (GaAs),aluminum gallium arsenide (AlGaAs); or semiconductor alloy, such assilicon germanium (SiGe), gallium arsenide phosphide (GaAsP). Theepitaxial processes for growing the semiconductor material may includeCVD deposition techniques (e.g., LPCVD, vapor-phase epitaxy (VPE) and/orultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or othersuitable processes. In an embodiment, the semiconductor material, suchas silicon carbon (SiC), is epi-grown by a LPCVD process to form thesource/drain regions 112 and 114 of an n-type finFET 100. The LPCVDprocess is performed at a temperature of about 400 to about 800° C. andunder a pressure of about 1 Torr to about 200 Torr, using Si₃H₈ andSiH₃CH as reaction gases. In another embodiment, the semiconductormaterial, such as silicon germanium (SiGe), is epi-grown by a LPCVDprocess to form source/drain regions 112 and 114 of a p-type finFET 100.The LPCVD process is performed at a temperature of about 400° C. toabout 800° C. and under a pressure of about 1 Torr to about 200 Torr,using SiH₄ and GeH₄ as reaction gases.

Source/drain regions 112 and 114 may be in-situ doped during theepitaxial growth of the semiconductor material. In various embodiments,the epitaxially grown source/drain regions 112 and 114 may be doped withp-type dopants, such as boron or BF₂; n-type dopants, such as phosphorusor arsenic; and/or combinations thereof; epitaxially grown SiGesource/drain regions 112 and 114 may be doped with p-type dopants, suchas boron or BF₂, n-type dopants, such as phosphorus or arsenic, and/orcombinations thereof; epitaxially grown Si source/drain regions 112 and114 may be doped with carbon to form Si:C source/drain features,phosphorous to form Si:P source/drain features, or both carbon andphosphorous to form SiCP source/drain features. In one embodiment,source/drain regions 112 and 114 are not in-situ doped, an ionimplantation process is performed to dope source/drain regions 112 and114. One or more annealing processes may be performed to activatesource/drain regions 112 and 114. Annealing processes include but arenot limited to rapid thermal annealing (RTA) and/or laser annealingprocesses.

Further illustrated in FIG. 8 are interfaces 856 between spacers 120 andsource/drain regions 112 and 114. In an embodiment, interfaces 856 arecoplanar with interfaces 652. In other embodiments, interfaces 856 areeither above or below interfaces 652.

FIGS. 9A-9B are cross-sectional views of the structure of FIG. 8 alonglines A-A and B-B, respectively, after exemplary formation of etch stoplayer 958 and interlayer dielectric (ILD) layer 960. Patternedpolysilicon structure 650 is disposed on top surfaces 106 t of STIregions 106 and is wrapped around upper fin portions 546.1 through546.3, as illustrated in FIG. 9A. Etch stop layer 958 is formed on sidesof spacers 120 and on top of source/drain regions 112 and 114, asillustrated in FIG. 9B. Etch stop layer 958 may be used as a mask layerand a protective layer to protect source/drain regions 112 and 114during formation of source/drain contact structures (not shown). In someembodiments, etch stop layer 958 is be formed of materials including,but not limited to, SiNx, SiOx, SiON, SiC, SiCN, BN, SiBN, SiCBN, andcombinations thereof. Etch stop layer 958 may be formed using plasmaenhanced chemical vapor deposition (PECVD), sub atmospheric chemicalvapor deposition (SACVD), low pressure chemical vapor deposition(LPCVD), ALD, high-density plasma (HDP), plasma enhanced atomic layerdeposition (PEALD), molecular layer deposition (MLD), plasma impulsechemical vapor deposition (PICVD), or other suitable deposition methods.In some embodiments, etch stop layer 958 includes a silicon nitride or asilicon oxide formed by a LPCVD, PECVD, or CVD process, or a siliconoxide formed by HARP. In an embodiment, etch stop layer 958 has athickness in a range from about 20 nm to 200 nm. In another embodiment,etch stop layer 958 has a thickness in a range from about 20 nm to about100 nm.

Further illustrated in FIG. 9B, ILD layer 960 is formed on etch stoplayer 958. Formation of ILD layer 960 may include deposition of adielectric material, followed by an annealing of the depositeddielectric material and planarization of the annealed dielectricmaterial. The dielectric material of ILD layer 960 may be depositedusing any deposition methods suitable for flowable dielectric materials(e.g., flowable silicon oxide, flowable silicon nitride, flowablesilicon oxynitride, flowable silicon carbide, or flowable siliconoxycarbide). For example, flowable silicon oxide may be deposited forILD layer 960 using FCVD process. A wet anneal process may performed onthe deposited dielectric material of ILD layer 960. An illustrative wetanneal process includes annealing ILD layer 960 in steam at atemperature in a range from about 200° C. to about 700° C. for a periodin a range from about 30 minutes to about 120 minutes. In an embodiment,the dielectric material is silicon oxide. The wet annealed dielectricmaterial of ILD layer 960 may then be planarized by chemical mechanicalpolishing (CMP). CMP of the wet annealed dielectric material forms ILDlayer 960 having top surface 960 a which is coplanar with top surface650 a of patterned polysilicon structure 650. During the CMP process, aportion of etch stop layer 958 above structure 648 is removed.

FIGS. 10A-15A and FIGS. 10B-15B show various stages of an exemplary gatereplacement process for finFET 100 to replace structure 648 with gatestructure 108. FIGS. 10A-10B show respective cross-sectional views ofthe structure of FIGS. 9A-9B after removal of patterned polysiliconstructure 650 followed by deposition of dielectric layer 116, accordingto some embodiments. Patterned polysilicon structure 650 may be removedby a dry etching process such as reactive ion etching (RIE). The gasetchants used in etching of polysilicon 650 may include chlorine,fluorine, bromine, and/or combinations thereof. FIG. 10A illustratesthat dielectric layer 116 is disposed on top surfaces 106 t of STIregions 106 and is wrapped around upper fin portions 546.1 through546.3. Dielectric layer 116 is also disposed along sidewalls 1062 a andbottom surface 1062 b of trench 1062 formed after removal of patternedpolysilicon structure 650, as shown in FIG. 10B. Dielectric layer 116may include one or more layers of silicon oxide, silicon nitride,silicon oxy-nitride, or high-k dielectric materials such as hafniumoxide (HfO₂), TiO₂, HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, or combinationsthereof. Dielectric layer 116 may be formed by CVD, ALD, PVD, e-beamevaporation, or other suitable process. Alternatively, high-k dielectricmaterials may comprise metal oxides. Examples of metal oxides used forhigh-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Al,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and/or mixturesthereof. The high-k dielectric layer may be formed by ALD and/or othersuitable methods.

FIGS. 11A-11B show respective cross-sectional views of the structure ofFIGS. 10A-10B after exemplary deposition of gate work function metallayer 222. Gate work function metal layer 222 is disposed on dielectriclayer 116. In some embodiments, gate work function metal layer 222includes any suitable material, such as Al, Cu, W, Ti, Ta, TiN, TaN,NiSi, CoSi, Ag, TaC, TaSiN, TaCN, TiAl, TiAlN, WN, metal alloys, and/orcombinations thereof. The one or more materials included in gate workfunction metal layer 222 may be formed using a suitable process such asALD, CVD, PVD, plating, or combinations thereof. In some embodiments,the deposited gate work function metal layer 222 has a thickness 222 tin the range of about 2 nm to about 15 nm.

FIGS. 12A-12B show respective cross-sectional views of the structure ofFIGS. 11A and 11B after exemplary deposition of gate metal liner 228.Gate metal liner 228 is disposed on gate work function metal layer 222.Gate metal liner 228 may include any suitable metal such as W, Al, Co,Ti, Ag, Al, Mn, Zr, Cu, Ni, and/or combinations thereof and may beformed by ALD, PVD, CVD, or other suitable metal deposition process.

FIGS. 13A-13B show respective cross-sectional views of the structure ofFIGS. 12A-12B after exemplary formation of gate metal oxide layer 226.In some embodiments, gate metal oxide layer 226 is formed on gate metalliner 228. Gate metal liner 228 may serve as a metal precursor for theformation of gate metal oxide layer 226. Gate metal oxide layer 226 maybe formed by oxidizing gate metal liner 228 using any suitable oxidationprocess such as, but not limited to, air oxidation (i.e., exposure toair), O₂ plasma process, or a wet or dry thermal oxidation in an ambientcomprising an oxide, H₂O, NO, or a combination thereof. In someembodiments, forming gate metal oxide layer 226 includes depositing gatemetal liner 228 in a deposition chamber, breaking vacuum in thedeposition chamber after deposition of gate metal liner 228, andexposing gate metal liner 228 to air for a period that ranges from about1 min to about 15 min. The air may be ambient air that is filtered byHEPA filters. In some embodiments, forming gate metal oxide layer 226includes depositing gate metal liner 228 in a deposition chamber,introducing oxygen into the deposition chamber, and thermally oxidizinggate metal liner 228 at an oxidation temperature of the materialincluded in gate metal liner 228. In some embodiments, surface and/orseveral topmost atomic layers of gate metal liner 228 is oxidized toform gate metal oxide layer 226. In other embodiments, gate metal liner228 is completely oxidized to form gate metal oxide layer 226, which isdisposed on gate work function metal layer 222 (not shown). Gate metaloxide layer 226 may include any suitable oxide of metals such as oxideof W, Al, Co, Ti, Ag, Al, Mn, Zr, Cu, Ni, and/or combinations thereof.

Gate metal oxide layer 226 may partially or completely fill the areasbetween fins 104.1 through 104.3 such as areas 230 and/or 232. In someembodiments, top surface portion 226 a of gate metal oxide layer 226within area 230 and/or top surface portion 226 b of gate metal oxidelayer 226 is below or coplanar with top surface portion 226 s of gatemetal oxide layer 226, top surface portion 222 s of gate work functionmetal layer 222, top surface portion 116 s of dielectric layer 116, ortop surfaces 104 s of fins 104.1 through 104.3. Top surface portions 226s, 222 s, 116 s are surface portions that are disposed over fins 104.1through 104.3. In some embodiments, top surface portions 226 a and/or226 b are above surface 222 s, surface 116 s, or top surface 104 s. Gatemetal oxide layer 226 may include voids or air pockets of differentshapes and sizes such as voids or air pockets 234. Even though voids orair pockets 234 are illustrated to be included only in a portion of gatemetal oxide layer 226 within area 230, the present disclosure is notlimited to this illustration. Voids or air pockets of any shape and sizeand in any number may be formed in any portion of gate metal oxide layer226. In some embodiments, gate metal oxide layer 226 is a continuouslayer and does not include voids or air pockets. In some embodiments,gate metal oxide layer 226 is formed only within areas 230 and 232 andnot over STI regions 106 and fins 104.1 through 104.3 (not shown).

FIGS. 14A-14B show respective cross-sectional views of the structure ofFIGS. 13A-13B after exemplary deposition of gate metal fill layer 224.Gate metal fill layer 224 is disposed on gate metal oxide layer 226.Gate metal fill layer 224 may include a single metallic layer or a stackof metallic layers. The stack of metallic layers may include metalsdifferent from each other. In some embodiments, gate metal fill layer224 includes any suitable conductive material, such as Ti, Ag, Al,TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, WN, Cu, W, Co, Ni,TiC, TiAlC, TaAlC, metal alloys, and/or combinations thereof. Gate metalfill layer 224 may be formed by ALL), PVD, CVD, or other suitableconductive material deposition process. In an embodiment, gate metalfill layer 224 includes W film formed by ALD or CVD. The W film mayinclude fluorine in the form of fluoride ions introduced from afluorine-based precursor (e.g., tungsten hexafluoride (WF₆)) used duringthe W film deposition process. In another embodiment, gate metal filllayer 224 includes Al or Co film formed by ALD or CVD.

Typically, in current gate replacement processes, fluorine from W-basedgate metal fill layer, Al from Al-based gate metal fill layer, Co fromCo-based gate metal fill layer, or other elements from other suitablemetal based gate metal fill layers diffuse or migrate into one or moreunderlying layers such as gate work function metal layers (e.g., gatework function metal layer 222), dielectric layers (e.g., dielectriclayer 116), fins (e.g., fins 104.1 through 104.3), and/or other layersand/or structures of current devices. The presence of such contaminantsin considerable amounts adversely affects the chemical and physicalproperties of the materials of the underlying layers of the currentdevices. For example, diffusion of fluorine contaminants in underlyinggate work function metal layers can negatively affect the work functionvalue of the one or more metals included in the gate work function metallayers of current devices, and consequently, have negative effect on thecontrol and tuning of the threshold voltage of the current devices. Gatemetal oxide layer 226 underlying gate metal fill layer 224 helps toovercome such problems of current gate replacement processes. Gate metaloxide layer 226 may act as a passivation layer to prevent and/or reducethe diffusion of unwanted and/or detrimental elements from gate metalfill layer 224 into one or more underlying layers such as gate workfunction metal layer 222, dielectric layer 116, fins 104.1 through104.3, and/or source/drain regions 112 and 114 during subsequentprocessing of finFET 100.

FIGS. 15A-15B show respective cross-sectional views of the structure ofFIGS. 14A-14B after exemplary planarization of gate metal fill layer224, gate metal oxide layer 226, gate metal liner 228, gate workfunction metal layer 222, and dielectric layer 116. Gate metal filllayer 224, gate metal oxide layer 226, gate metal liner 228, gate workfunction metal layer 222, and dielectric layer 116 may be planarizedusing a CMP process. In an embodiment, ILD layer 960 acts as aplanarization stop layer during planarizing of these layers. CMP removesexcess portions of gate metal fill layer 224, gate metal oxide layer226, gate metal liner 228, gate work function metal layer 222, anddielectric layer 116, such that top surfaces 224 s, 226 s, 228 s, 222 s,and 116 s of gate metal fill layer 224, gate metal oxide layer 226, gatemetal liner 228, gate work function metal layer 222, and dielectriclayer 116, respectively, are coplanar with top surface 960 s of ILD 960.It should be noted that even though gate metal liner 228 is shown ingate replacement process of FIGS. 14A-15A and 14B-15B, a person skilledin the art(s) would understand that gate metal liner 228 may not bepresent at these stages of the gate replacement process if gate metalliner 228 is completely oxidized to form gate metal oxide layer 226during the oxidation process of gate metal liner 228.

Formation of gate structure 108 shown in FIGS. 15A and 15B may befollowed by formation of other elements such as source/drain contacts,gate contacts, vias, interconnect metal layers, dielectric layers,passivation layers, etc., that are not shown for the sake of clarity.

FIG. 16 shows a TEM image of a cross-section of an exemplary teststructure 100* across fins 104.1* through 104.3* and structure 108*. Insome embodiments, fins 104.1* through 104.3* and structure 108* may besimilar to fins 104.1 through 104.3 and gate structure 108 describedabove. Similar to the gate replacement process described above withrespect to FIGS. 10A-15A and 10B-15B, formation of structure 108*includes depositing a W-based metal liner using an ALD process followedby vacuum break and oxidation of the W-based metal liner in air. Theoxidation process forms W-based metal oxide 226* within areas 230* and232* between fins 104.1* through 104.3*. W-based metal oxide 226* may besimilar to gate metal oxide layer 226 described above. The oxidationstep is followed with a deposition of a W-based metal fill layer 224*,which may be similar to gate metal fill layer 224 described above.

In contrast to test structure 100*, FIG. 17 shows a TEM image of across-section of another test structure 100** through fins 104.1** and104.2** and structure 108** where formation of structure 108** includesdepositing a W-based metal liner and a W-based metal fill layer in-situusing ALD, that is without breaking vacuum between the depositions. Assuch, areas 230** and 232** between fins 104.1** and 104.2** are notfilled with oxidized W metal liner.

FIGS. 18 and 19 show EDX element maps for tungsten (W) and oxygen (O),respectively, in a cross-section of exemplary test structure 100* acrossfins 104.1* through 104.3* and structure 108*. The maps are obtainedafter the formation of W-based metal oxide 226*. The formation ofW-based metal oxide 226* within areas 230* and 232* between fins 104.1*through 104.3* is confirmed from the W and O EDX maps. FIG. 18 shows thepresence of W within areas 230* and 232*. FIG. 19 shows the presence ofO within areas 230* and 232*. FIGS. 18 and 19 also show the presence ofW and O over fins 104.1* through 104.3*. This presence may indicate theformation of W-based metal oxide 226* in at least one or more regionsover fins 104.1* through 104.3*.

Example Operations for Fabricating a FinFET According to an Embodiment

FIG. 20 is a flow diagram of an exemplary method 2000 for fabricatingfinFET 100. Solely for illustrative purposes, the operations illustratedin FIG. 20 will be described with reference to the example fabricationprocess illustrated in FIGS. 3-8, FIGS. 9A-15A, and 9B-15B. Operationscan be performed in a different order or not performed depending onspecific applications. It should be noted that method 2000 does notproduce a completed finFET 100. Accordingly, it is understood thatadditional processes may be provided before, during, and after method2000, and that some other processes may only be briefly describedherein.

In operation 2010, an ILD layer is formed over fins and isolationregions. For example, an ILD layer such as ILD layer 960 is formed onfins 104.1 through 104.3 and STI regions 106. Formation of ILD layer 960may include deposition of a dielectric material, followed by anannealing of the deposited dielectric material and planarization of theannealed dielectric material. The dielectric material of ILD layer 960may be deposited using any deposition methods suitable for flowabledielectric materials. For example, flowable silicon oxide is depositedfor ILD layer 960 using FCVD process. A wet anneal process may performedon the deposited dielectric material of ILD layer 960. The wet annealeddielectric material of ILD layer 960 may then be planarized by CMP.

In operation 2020, a patterned polysilicon structure is removed. Forexample, patterned polysilicon structure 650 may be removed by a dryetching process such as reactive ion etching (RIE). In some embodiments,the gas etchants used in etching of patterned polysilicon structure 650may include chlorine, fluorine, bromine, and/or combinations thereof.

In operation 2030, a dielectric layer is deposited on the fins and theisolation regions. For example, a dielectric layer such as dielectriclayer 116 is disposed on top surfaces 106 t of STI regions 106 andwrapped around upper fin portions 546.1 through 546.3. Dielectric layer116 may also be disposed along sidewalls 1062 a and bottom surface 1062b of trench 1062 formed after removal of patterned polysilicon structure650 in operation 2020. Dielectric layer 116 may be formed by CVD, ALD,PVD, e-beam evaporation, or other suitable process.

In operation 2040, a gate work function metal layer is deposited on thedielectric layer of operation 2030. For example, a gate work functionmetal layer such as gate work function metal layer 222 is disposed ondielectric layer 116 using a suitable process such as ALD, CVD, PVD,plating, or combinations thereof.

In operation 2050, a gate metal liner is deposited on the gate workfunction metal layer of operation 2040. For example, a gate metal linersuch as gate metal liner 228 is disposed on gate work function metallayer 222 using a suitable process such as ALD, PVD, CVD, or othersuitable metal deposition process.

In operation 2060, a gate metal oxide layer is formed on the gate metalliner of operation 2050. For example, a gate metal oxide layer such asgate metal oxide layer 226 is formed on gate metal liner 228. Gate metaloxide layer 226 may be formed by oxidizing gate metal liner 228 usingany suitable oxidation process such as, but not limited to, airoxidation (i.e., exposure to air), O₂ plasma process, or a wet or drythermal oxidation in an ambient comprising an oxide, H₂O, NO, or acombination thereof.

In operation 2070, a gate metal fill layer is formed on the gate metaloxide layer of operation 2060. For example, a gate metal fill layer suchas gate metal fill layer 224 is disposed on gate metal oxide layer 226.Gate metal fill layer 224 may be formed by ALD, PVD, CVD, or othersuitable conductive material deposition process.

In operation 2080, the gate metal fill layer, the gate metal oxide, thegate metal liner, the gate work function metal layer, and the dielectriclayer of operations 2070, 2060, 2050, 2040, and 2030 are planarized. Forexample, gate metal fill layer 224, gate metal oxide 226, gate metalliner 228, gate work function metal layer 222, and dielectric layer 116may be planarized using CMP. The CMP may coplanarize top surfaces 224 s,226 s, 228 s, 222 s, and 116 s of gate metal fill layer 224, gate metaloxide 226, gate metal liner 228, gate work function metal layer 222, anddielectric layer 116, respectively, with top surface 960 s of ILD 960.

Thus, the present disclosure provides a modified gate replacementprocess for a semiconductor device to prevent and/or reduce diffusion ofunwanted and/or detrimental elements from a gate metal fill layer intoits underlying layers during the gate replacement process and/or duringsubsequent processing of the semiconductor device. The mechanismsprovided herein help to reduce diffusion surface area for unwantedand/or detrimental elements to diffuse from a gate metal fill layer intounderlying layers such as gate work function layer(s), gate dielectriclayer(s), and/or fin structure(s) of the semiconductor device to improveits device performance. In one embodiment, the mechanism includesoxidizing a gate metal liner deposited on a gate work function layer,followed by deposition of a gate metal fill layer on the oxidized metalliner. The oxidized gate metal liner provides a passivation layer andreduces the diffusion surface area between the gate metal fill layer andits underlying layers. Reduction of the diffusion surface area helps toreduce the negative impact of the unwanted and/or detrimental elementson the material properties and consequently, the electrical performanceof layers underlying the gate metal fill layer of the semiconductordevice.

Example Embodiments and Benefits

In an embodiment, a method of forming a semiconductor device includesforming a plurality of fins on a substrate, forming a polysilicon gatestructure, and replacing the polysilicon gate structure with a metalgate structure. The replacing of the polysilicon gate structure includesdepositing a work function metal layer over the plurality of fins,forming a metal oxide layer over the work function metal layer, anddepositing a first metal layer over the metal oxide layer. A firstportion of the metal oxide layer is formed within an area betweenadjacent fins from among the plurality of fins. An exemplary benefit ofthis embodiment is the prevention and/or reduction of diffusion ofunwanted and/or detrimental elements from a gate metal fill layer intoits underlying layers and consequently, the reduction of the negativeimpact of these unwanted and/or detrimental elements on the deviceperformance.

In a further embodiment, a method includes forming a plurality of finson a substrate, forming a polysilicon structure, and replacing thepolysilicon structure with a gate structure. Replacing the polysiliconstructure includes depositing a work function metal layer over theplurality of fins, forming a passivation layer over the work functionmetal layer, and depositing a first metal layer over the passivationlayer. A portion of the passivation layer is formed within an areabetween adjacent fins from among the plurality of fins. Anotherexemplary benefit of this embodiment is the prevention and/or reductionof diffusion of unwanted and/or detrimental elements from a gate metalfill layer into its underlying layers and consequently, the reduction ofthe negative impact of these unwanted and/or detrimental elements on thedevice performance.

In a still further embodiment, a semiconductor device includes aplurality of fins on a substrate and a replacement gate structure. Thereplacement gate structure includes a dielectric layer disposed on theplurality of fins, a work function metal layer disposed on thedielectric layer, and a passivation layer disposed over the workfunction metal layer. A portion of the passivation layer is disposedwithin an area between adjacent fins from among the plurality of fins.The replacement gate structure further includes a metal fill layerdisposed on the passivation layer An exemplary benefit of thisembodiment is the prevention and/or reduction of diffusion of unwantedand/or detrimental elements from a gate metal fill layer into itsunderlying layers and consequently, the reduction of the negative impactof these unwanted and/or detrimental elements on the device performance.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming a plurality of fins on a substrate; forming apolysilicon gate structure on the plurality of fins; and replacing thepolysilicon gate structure with a metal gate structure, wherein thereplacing comprises: depositing a work function metal layer over theplurality of fins; depositing a first metal layer over the work functionmetal layer; forming a metal oxide layer over the first metal layer,wherein a portion of the metal oxide layer fills an area betweenadjacent fins of the plurality of fins; and depositing a second metallayer on the metal oxide layer, wherein the metal oxide layer prevents adiffusion of elements from the second metal layer into the work functionmetal layer.
 2. The method of claim 1, wherein the forming the metaloxide layer comprises oxidizing the first metal layer.
 3. The method ofclaim 1, wherein the forming the metal oxide layer comprises oxidizingthe first metal layer in air, oxygen plasma, water, nitric oxide, or acombination thereof.
 4. The method of claim 1, wherein the portion ofthe metal oxide layer comprises voids or air pockets.
 5. The method ofclaim 1, wherein another portion of the metal oxide layer is formed overthe plurality of fins.
 6. The method of claim 1, wherein an interfacebetween the metal oxide layer and the second metal layer is formed belowor coplanar with a top surface of at least one fin of the plurality offins.
 7. The method of claim 1, further comprising forming an interlayerdielectric layer (ILD) over the plurality of fins.
 8. The method ofclaim 7, wherein the replacing the polysilicon gate structure furthercomprises planarizing the second metal layer, the metal oxide layer, thefirst metal layer, and the work function metal layer to be coplanar witha top surface of the ILD layer.
 9. The method of claim 1, wherein thesecond metal layer comprises tungsten, aluminum, or cobalt.
 10. Themethod of claim 1, wherein the first metal layer comprises tungsten (W),aluminum (Al), cobalt (Co), titanium (Ti), silver (Ag), manganese (Mn),zirconium (Zr), copper (Cu), nickel (Ni), or a combination thereof. 11.A method, comprising: forming a plurality of fins on a substrate;forming a polysilicon structure on the plurality of fins; and replacingthe polysilicon structure with a gate structure, wherein the replacingcomprising: depositing a work function metal layer over the plurality offins; depositing a first metal layer over the work function metal layer;forming a passivation layer over the first metal layer, wherein aportion of the passivation layer fills an area between adjacent fins ofthe plurality of fins; and depositing a second metal layer on thepassivation layer, wherein the passivation layer prevents a diffusion ofelements from the second metal layer into the work function metal layer.12. The method of claim 11, wherein the portion of the passivation layercomprises voids or air pockets.
 13. The method of claim 11, wherein thepassivation layer comprises a metal oxide.
 14. The method of claim 11,wherein the forming the passivation layer comprises oxidizing the firstmetal layer in air, oxygen plasma, water, nitric oxide, or a combinationthereof.
 15. The method of claim 11, wherein the passivation layercomprises a metal oxide of tungsten (W), aluminum (Al), cobalt (Co),titanium (Ti), silver (Ag), manganese (Mn), zirconium (Zr), copper (Cu),nickel (Ni), or a combination thereof.
 16. A method of forming asemiconductor device, the method comprising: forming a plurality of finson a substrate; depositing a work function metal layer over theplurality of fins; depositing a first metal layer over the work functionmetal layer; forming a diffusion barrier layer over the first metallayer, a portion of the diffusion barrier layer being formed within anarea between adjacent fins of the plurality of fins; and depositing asecond metal layer on the diffusion barrier layer, wherein the diffusionbarrier layer prevents a diffusion of elements from the second metallayer into the work function metal layer.
 17. The method of claim 16,wherein the forming the diffusion barrier layer comprises oxidizing thefirst metal layer.
 18. The method of claim 16, wherein the forming thediffusion barrier layer comprises oxidizing the first metal layer inair, oxygen plasma water, nitric oxide, or a combination thereof. 19.The method of claim 16, wherein the portion of the diffusion barrierlayer comprises voids or air pockets.